WASHINGTON  Pollution from electrical generators, compressors, agricultural pumps and other equipment powered by stationary diesel engines would drop by as much as 90 percent under a government proposal, The Associated Press has learned.

Beginning in 2007, companies would have to produce cleaner-burning diesel engines for use in such equipment. Operators would have to start using lower sulfur fuel at that time and switch to even better grades by 2011.

The Environmental Protection Agency planned to make the proposal public on Thursday.

It stems from a court agreement with Environmental Defense, a New York-based advocacy group that sued in federal court in California in 2003, saying the federal standards were long overdue.

Agency officials declined comment before the proposed rule had been signed to meet Wednesday's court-ordered deadline.

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About 600,000 stationary diesel engines are estimated to be in use; more than half of them are electrical generators.

The EPA's proposal would affect about 100,000 new stationary diesel engines made each year.

"Reducing the pollution from diesel exhaust is one of the single most important steps that can be taken to protect human health from harmful air pollution," said Jana Milford, a senior scientist with Environmental Defense.

Engine owners would be expected to use diesel fuel that contains up to 500 parts per million of sulfur starting in 2007, then switch again to fuel with up to 15 ppm of sulfur in 2011, according to the group.

Currently, some types of diesel fuel used in off-road vehicles and some stationary equipment can contain up to 5,000 ppm of sulfur.

A similar rule issued last year was intended to cut pollution by more than 90 percent from off-road vehicles and equipment such as forklifts, farm tractors and tugboats.

Environmental Defense said the latest proposal would close "a critical gap," because existing stationary diesel engines discharge pollution at levels 10 times to 20 times higher than national emission standards would allow for their mobile source counterparts.

It is intended to cut tens of thousands of tons of smog-forming chemicals, fine particles and soot annually, which are blamed each year for increases in respiratory illnesses and thousands of premature deaths. Those considered especially vulnerable are children, the elderly and people suffering from asthma.

The one big exception is for diesel engines in emergency backup generators used by apartment and commercial buildings, hotels, banks and other businesses concerned about power outages, said Environmental Defense's director of special projects. Mark MacLeod.

That is because those engines are typically used only a couple hours a month to make sure they still operate reliably, he said.

Several states, including Texas and California, previously adopted emission standards for stationary engines. The Senate voted last week to provide a $1 billion fund for grants and loans to cut pollution from existing diesel engines.

The new proposal "is really the continuation of applying the clean diesel system to all categories of diesel machines and vehicles," said Bill Buff, spokesman for the Diesel Technology Forum, an industry group for engine makers, refiners and manufacturers of pollution-control devices.

"It started with trucks and buses, which in January 2007 are going to be 98 percent cleaner than back in late '80s."